It is known that the flame resistance of aromatic polycarbonates can be improved by adding salts of organic or inorganic acids, such as, the alkali metal salts. Such flame-resistant polycarbonates are described, for example, in German Offenlegungsschrift 1,930,257 (LeA 12,278), German Offenlegungsschrift 2,149,311 (LeA 13,999) and German Offenlegungsschrift 2,744,018.
Such salts have hitherto been incorporated either directly into the melt of the polycarbonates or by combining them with the polycarbonate solution, a solution of the salts in organic solvents being preferred in the latter case (see German Offenlegungsschrift No. 2,460,052 (LeA 19,004)). However, the disadvantage of the procedure is that most of the flameproofing agents for polycarbonates are substantially insoluble in the organic phase suitable for the preparation of the polycarbonates.
It is known, see U.S. Pat. No. 4,113,695, that in order to preserve the optical properties of polycarbonates upon rendering them flame resistant, it is preferable to use an aqueous solution, rather than a powdered form, of the flameproofing agents. The solution is thus applied to the surface of the resin followed by drying and by extrusion. Compared with the conventional processes, in which solid flameproofing agents are incorporated into the polycarbonates by mixing, the above process is deficient in terms of distribution and hence efficiency of the agents used.
It was thus unexpected that aqueous solutions of flameproofing agents could be distributed in the polycarbonate via an organic phase to such an extent that their activity becomes superior to that of flameproofing agents metered-in conventionally as solids.